U.S. patent application number 17/108846 was filed with the patent office on 2021-06-10 for device and method for angle stabilization of a virtual synchronous machine.
The applicant listed for this patent is Wobben Properties GmbH. Invention is credited to Sonke Engelken, Marco Liserre, Roberto Rosso.
Application Number | 20210172418 17/108846 |
Document ID | / |
Family ID | 1000005288219 |
Filed Date | 2021-06-10 |
United States Patent
Application |
20210172418 |
Kind Code |
A1 |
Rosso; Roberto ; et
al. |
June 10, 2021 |
DEVICE AND METHOD FOR ANGLE STABILIZATION OF A VIRTUAL SYNCHRONOUS
MACHINE
Abstract
Provided is a control circuit of a converter, in particular a
power converter of a wind power installation, configured to control
the converter in such a way that the converter emulates a behavior
of a synchronous machine. The control circuit includes a power
module for calculating a power change depending on a detected power
and a correction module for setting a power set point, in
particular for the converter, depending on the calculated power
change.
Inventors: |
Rosso; Roberto; (Aurich,
DE) ; Engelken; Sonke; (Bremen, DE) ; Liserre;
Marco; (Kiel, DE) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Wobben Properties GmbH |
Aurich |
|
DE |
|
|
Family ID: |
1000005288219 |
Appl. No.: |
17/108846 |
Filed: |
December 1, 2020 |
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
F03D 7/028 20130101;
G05B 2219/41294 20130101; G05F 1/66 20130101; F03D 9/25 20160501;
H02P 2101/15 20150115; H02J 2300/28 20200101 |
International
Class: |
F03D 7/02 20060101
F03D007/02; F03D 9/25 20060101 F03D009/25 |
Foreign Application Data
Date |
Code |
Application Number |
Dec 10, 2019 |
DE |
102019133813.1 |
Claims
1. A control circuit of a converter configured to control the
converter to cause the converter to emulate a synchronous machine,
comprising: a power circuit configured to determine a power change
depending on a detected power; and a correction circuit configured
to set a power set point for the converter depending on the power
change.
2. The control circuit as claimed in claim 1, wherein the converter
is a power converter of a wind power installation.
3. The control circuit as claimed in claim 1, comprising: a power
angle circuit configured to determine a power angle change
depending on at least one detected frequency, wherein: the
correction circuit is configured to set the power set point
depending on the power angle change.
4. The control circuit as claimed in claim 3, wherein the power
angle circuit includes: a subtractor configured to determine a
frequency difference based on comparing at least one first
electrical frequency with a second electrical frequency.
5. The control circuit as claimed in claim 4, wherein the power
angle module includes: at least one limiter configured to limit the
frequency difference to a positive value.
6. The control circuit as claimed in claim 3, further comprising: a
multiplier configured to multiply the power change and the power
angle change to form a coefficient, wherein the correction circuit
is configured to set the power set point depending on the
coefficient.
7. The control circuit as claimed in claim 6, wherein the
correction circuit is configured to only set the power set point if
the coefficient exceeds a predetermined threshold value.
8. The control circuit as claimed in claim 1, wherein the power
circuit includes: at least one discrete processor configured to
determine, discretely, numerically or digitally, a derivative of
the detected power.
9. The control circuit as claimed in claim 8, wherein the power
circuit includes: at least one discrete filter, coupled to an
output of the discrete processor, configured to determine the power
change.
10. The control circuit as claimed in claim 1, wherein the power
circuit includes: at least one observer configured to determine the
power change.
11. The control circuit as claimed in claim 10, wherein: the
observer is a proportional-integral (PI) controller, and the
observer is configured to determine the power change based on a
difference between the detected power and an estimated power that
is estimated by the observer.
12. A controller of the converter, comprising: the control circuit
as claimed in claim 1.
13. The converter as claimed in claim 13, comprising: the
controller configured to control the converter.
14. The converter as claimed in claim 13, wherein the controller is
for a virtual synchronous machine.
15. A wind power installation, comprising: the converter as claimed
in claim 13.
16. A method for controlling a power converter of a wind power
installation to emulate a synchronous machine, comprising:
detecting a power at an output of the power converter; calculating
a power change depending on the detected power; and setting a power
set point for the power converter depending on the calculated power
change.
17. The method for controlling the power converter as claimed in
claim 16, comprising: determining a power angle change depending on
at least one detected frequency; and setting the power set point
depending on the power angle change.
18. The method for controlling the power converter as claimed in
claim 17, comprising: multiplying the power change and the power
angle change to produce a coefficient; and setting the power set
point depending on the coefficient.
19. The method for controlling the power converter as claimed in
claim 18, wherein the coefficient which has the same sign as a
synchronizing power coefficient.
20. The method for controlling the power a converter as claimed in
claim 17, comprising: determining the power angle change at least
by comparing a mechanical frequency and an electrical frequency.
Description
BACKGROUND
Technical Field
[0001] The present invention relates to a control module (control
circuit or control stage) of a converter, in particular a power
converter of a wind power installation, which is set up to control
the converter in such a way that the converter emulates a behavior
of a synchronous machine. The present invention further relates to
a control unit (controller) which has a control module of this
type, a converter which has a control module of this type as well
as a method for controlling the converter and a wind power
installation which has a control module of this type and/or carries
out a method of this type.
Description of the Related Art
[0002] Owing to the increasing displacement of conventional
synchronous generator driven power plants by regenerative,
converter-based generators, classical synchronous generators are
losing more and more influence within the electrical supply
network.
[0003] This decline in synchronous generators also results in a
reduction in conventional flywheel masses which stabilize the
electrical supply network.
[0004] Since the effects of a change of this type within the
electrical supply network are virtually unexplored, there are some
considerations to operate the converters of the regenerative
generators in such a way that they operate like a synchronous
machine on the electrical supply network. In other words, the
converters should emulate the behavior of a synchronous machine,
without losing the benefits of power converter technology.
Converters which are operated in this manner are also referred to
as virtual synchronous machines.
[0005] In recent years, a wide variety of control methods have been
proposed for synchronous machine emulations for this purpose.
[0006] Some of these methods, as shown in R. Rosso, J. Cassoli, G.
Buticchi, S. Engelken, and M. Liserre, "Robust stability analysis
of LCL filter based synchronverter under different grid
conditions," IEEE Trans. Power Electron., 2018, doi: 10.11
09/TPEL.2018.2867040, for example, even have advantages over
standard established converter control methods, in particular on so
called weak networks.
[0007] A disadvantage of the previously known methods for emulating
a synchronous machine by means of a converter is that they are not
designed for any network errors which occur in the electrical
supply network.
BRIEF SUMMARY
[0008] A control method for controlling network errors for virtual
synchronous machines is provided preferably in order to continue to
be able to reproduce the characteristics of an actual synchronous
machine even in the case of a network error and under the
constraints of the hardware characteristics of the converter. In
particular, a method shall be proposed which identifies a critical
state with regard to angular stability and allows appropriate
measures to be taken.
[0009] A control module of a converter, in particular a power
converter of a wind power installation, is thus proposed which is
set up to control the converter in such a way that the converter
emulates a behavior of a synchronous machine, at least comprising:
a power module (circuit) for calculating a power change depending
on a detected power and a correction module (circuit) for setting a
power set point, in particular for the converter, depending on the
calculated power change.
[0010] The control module is set up in particular by means of the
power module and the correction module to identify a possible loss
of angular stability of the converter with regard to the electrical
supply network.
[0011] The converter is a converter of a wind power installation or
a photovoltaic installation, for example. The converter is
preferably a power converter, i.e., a converter which is set up and
used to feed electrical power into the electrical supply network.
For this purpose, the converter preferably has at least one DC link
voltage of at least 400V, further preferably of at least 690V, in
particular of at least 1000V.
[0012] The converter is therefore preferably designed as a power
converter of a wind power installation.
[0013] The converter itself is preferably controlled via a control
unit which comprises the control module described previously or
hereinafter and/or is controlled as described hereinafter.
[0014] The control module itself therefore has at least one power
module and a correction module.
[0015] The power module is set up to calculate a power change
depending on a detected power. The detected power is preferably the
electrical power which is emitted from the converter, in particular
to the electrical supply network. The power emitted from the
converter can be detected or determined by means of a power
detection at the output of the converter, for example. For this
purpose, the power detection itself can be a component of the
control unit of the converter or the control module, for
example.
[0016] The power change can further be determined over time by
means of a plurality of measurements, for example, i.e., a first
measurement at a first point in time and a second measurement at a
second point in time, for example. A difference can then be formed
from these two values recorded in this way, which difference
specifies the power change.
[0017] The power change is preferably determined by means of a
discrete implementation of the derivative of the measured or
detected power, preferably using a cascaded discrete filtering.
[0018] Alternatively, the power change is determined by means of an
observer which acts on the difference between the measured power
and an estimated power by way of a PI controller, for example.
[0019] The correction module is further set up to set a power set
point or to output a power set point, in particular in order to set
the power set point for the converter. In this case, the power set
point or the correction value for the power set point is determined
depending on the calculated power change.
[0020] The correction module preferably additionally has a
threshold value and only establishes a power set point for the
converter if the power change has exceeded a predetermined
threshold value.
[0021] The correction module can additionally have further
submodules and/or further modules are provided which are set up to
change and/or specify a power set point by means of a proportional
coefficient or a limitation to a fixed value, for example.
[0022] It has indeed been recognized that if the power change
exceeds a certain amount, in particular is negative, i.e., is
dP/dt<0, an angular instability can be present. In order to
verify the presence of an angular instability, the acceleration of
the virtual pole wheel is preferably taken as a basis, in
particular if this acceleration is positive, i.e.,
d.delta./dt>0, an angular instability or an imminent loss of
stability can be assumed. In particular, an angular instability
could be present if the product of these two coefficients exceeds
or falls below a certain limit. In such a case, the correction
module therefore intervenes in the control of the converter, in
order to specify a new power set point, in particular a more stable
power set point, for the converter.
[0023] It is therefore also proposed that the control module only
intervenes in the control of the converter after certain power
changes, in particular via the correction module.
[0024] The control module preferably further comprises a power
angle module for calculating a power angle change depending on at
least one detected frequency, wherein the power set point is also
set depending on the power angle change.
[0025] The control module therefore also has a power angle
module.
[0026] In this case, the power angle module is set up to determine
a power angle change depending on at least one detected
frequency.
[0027] The detected frequency can be a mechanical or an electrical
frequency, for example. At least one frequency of the virtual
synchronous machine and the frequency of the electrical supply
network are preferably detected.
[0028] The power angle change is therefore used, in precisely the
same manner as the power change, to determine the power set point
for the converter.
[0029] For this purpose, the power change dP/dt and the power angle
change d.delta./dt are preferably multiplied together.
[0030] In particular, it is therefore proposed that a coefficient
is calculated which has the same sign as the synchronizing power
coefficient. This is due to the fact that the sign of the
synchronizing power coefficient per se is already an indicator of a
possible angular instability. The proposed solution therefore has
the advantage that a division by zero can be avoided. The fact
should also be emphasized here that the coefficient d.delta./dt is
limited by a saturation block of [0, +.infin.] so that the
situation dP/dt>0 and d.delta./dt<0 (the product of which
also has a negative sign) is not identified as a critical
state.
[0031] The control module preferably further comprises a
multiplication by means of which the power change and the power
angle change are combined to form one product or coefficient,
wherein the power set point is also set depending on the
coefficient.
[0032] The power change and the power angle change are thus
multiplied to form one product which is used as a coefficient, in
particular in order to set the power set point for the
converter.
[0033] In particular, it is therefore proposed to generate a
coefficient by means of a multiplication, which coefficient is
indicative of the angular stability or indicates an imminent loss
of angular stability.
[0034] The power set point, in particular of the converter, is then
preferably set depending on this coefficient.
[0035] If a multiplication of this type is used which multiplies
the power angle change by the power change, it is also proposed
that the correction module has or comprises a corresponding
threshold value for this product.
[0036] The power module preferably has at least one discrete
implementation of a derivative of the detected power.
[0037] In particular, this means that the power module is set up to
determine the power change with respect to time, i.e., in
particular as a differential dP/dt.
[0038] For this purpose, the power module preferably has at least
one discrete filtering which is downstream of the discrete
implementation of the derivative of the detected power, in order to
determine the power change.
[0039] In particular, a discrete implementation of the derivative
of the measured power is therefore also proposed for determining
the power change, which implementation cooperates with an
additional cascaded discrete filtering.
[0040] Alternatively, the power module has at least one observer
which determines the power change dP/dt.
[0041] This can take place by way of a PI controller, for example,
which acts on the difference between a measured or detected power
and an estimated power and calculates a state variable dP.sub.dt as
a result.
[0042] The observer preferably acts on a difference between the
detected power and an estimated power, in particular estimated by
the observer, by way of a PI controller.
[0043] The power angle module preferably has at least one summation
which is set up to compare at least one first electrical frequency
with a second electrical frequency.
[0044] The summation preferably forms a difference from the
electrical frequency of the virtual synchronous machine and the
electrical frequency of the electrical supply network.
[0045] In particular, it is therefore proposed to take into account
both the electrical frequency of the virtual synchronous machine
and the electrical frequency of the electrical supply network, in
particular in order to calculate a frequency difference, namely the
electrical frequency of the virtual synchronous machine minus the
electrical frequency of the electrical supply network.
[0046] The power angle module preferably has at least one limiter
which is set up to limit the frequency difference to positive
values.
[0047] In particular, it is therefore proposed to only consider
positive values with regard to the power angle change.
[0048] For this purpose, the power angle change is guided via a
saturation block or is limited to exclusively positive values.
[0049] If negative values are therefore present, a zero is output
by the limiter or saturation block which results in the product of
the power angle change and power change also being zero, whereby
the threshold value of the correction module is not exceeded and
the set points thus do not change, in particular because there is a
stable operation.
[0050] In particular, it is therefore also proposed that only the
situations in which the power angle .delta. accelerates and the
power P decreases are identified as a critical state.
[0051] The correction module is preferably set up to only set the
power set point if a predetermined threshold value is exceeded, in
particular if the coefficient exceeds the predetermined threshold
value.
[0052] In particular, it is therefore also proposed that the
control module only intervenes in the control of the converter if
there is a risk of angular instability.
[0053] An angular instability is preferably always present if the
angle accelerates, i.e., the angle change is positive, and the
power decreases, i.e., the power change is negative.
[0054] As soon as a critical state is identified, the proposed
measure is to adjust the power set points, in particular of the
converter, to a lower value. This change preferably causes a
reduction in the power angle .delta. and prevents unstable
operation of the converter.
[0055] A control unit of a converter is further proposed, in
particular a power converter of a wind power installation,
comprising a control module described previously or
hereinafter.
[0056] In this case, the control unit is in particular set up to
generate current set points, by means of which the converter is
controlled, for example by means of a tolerance band method.
[0057] A method for controlling a converter is further proposed, in
particular a power converter of a wind power installation, wherein
the converter is set up to emulate the behavior of a synchronous
machine, comprising the steps: detecting a power at the output of
the converter, calculating a power change depending on the detected
power and setting a power set point, in particular for the
converter, depending on the calculated power change.
[0058] In particular, the method therefore makes provision for
controlling a converter, which is set up to emulate the behavior of
a synchronous machine, depending on a calculated power change.
[0059] In this case, the method is in particular additionally used
for control and is used in particular to reduce the power output of
the converter in critical cases, i.e., in particular if there is a
risk of loss of angular stability.
[0060] The method preferably further comprises the step:
calculating a power angle change depending on at least one detected
frequency, wherein the power set point is also set depending on the
power angle change.
[0061] The method preferably further comprises the step:
multiplying the power change and the power angle change to a
coefficient or product, wherein the power set point is also set
depending on the coefficient.
[0062] In particular, it is therefore also proposed that both the
power change and the power angle change are considered for
controlling the converter.
[0063] The power angle change is preferably determined at least by
comparing a first electrical frequency with a second electrical
frequency.
[0064] In particular, this takes place as described previously or
hereinafter.
[0065] A converter is further proposed, in particular a power
converter of a wind power installation, comprising at least one
control unit, in particular comprising a control module described
previously or hereinafter, wherein the control unit is set up to
control the converter in such a way that the converter emulates at
least one behavior of a synchronous machine and/or carries out a
method described previously or hereinafter.
[0066] The converter preferably comprises a control unit of a
virtual synchronous machine, in particular as described previously
or hereinafter.
[0067] A wind power installation is further proposed, comprising a
control module described previously or hereinafter and/or a control
unit described previously or hereinafter and/or a converter
described previously or hereinafter and/or a control unit of a
converter which is set up to carry out a method described
previously or hereinafter.
BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS
[0068] The present invention is explained in greater detail
hereinafter in an exemplary manner using exemplary embodiments with
reference to the accompanying figures, wherein the same reference
numbers are used for the same or similar components.
[0069] FIG. 1A shows a schematic view of a wind power installation
according to an embodiment.
[0070] FIG. 1B schematically shows the control unit of a virtual
synchronous machine.
[0071] FIG. 2 shows a control module of a converter in an
embodiment.
[0072] FIG. 3 shows a control module of a converter in a preferred
embodiment.
[0073] FIG. 4 shows a control module of a converter in a
particularly preferred embodiment.
[0074] FIG. 5 shows a power module of a control module in a
preferred embodiment.
[0075] FIG. 6 shows a power module of a control module of a
further, preferred embodiment.
DETAILED DESCRIPTION
[0076] FIG. 1A shows a schematic view of a wind power installation
100 according to an embodiment.
[0077] The wind power installation 100 comprises a tower 102 and a
nacelle 104. An aerodynamic rotor 106 with three rotor blades 108
and a spinner 110 is arranged on the nacelle 104. The rotor 106 is
transferred into a rotational movement by the wind during operation
and thus drives a generator in the nacelle 104.
[0078] The generator is connected to an electrical network, for
example a wind park network or an electrical supply network, by
means of a converter, in order to feed in a three-phase alternating
current.
[0079] For this purpose, the wind power installation comprises a
control module (circuit) described previously or hereinafter and/or
a control unit described previously or hereinafter and/or a
converter described previously or hereinafter and/or a control unit
of a converter which is set up to carry out a method described
previously or hereinafter.
[0080] FIG. 1B schematically shows the control unit 300 of a
virtual synchronous machine.
[0081] By means of this control unit 300, the converter 200 of the
wind power installation 100, as shown in FIG. 1A, for example, can
be controlled in such a way that the converter 200 emulates the
behavior of a synchronous machine.
[0082] For this purpose, the control unit 300 comprises an active
power control 310, a reactive power control 320, a processing unit
(processor) 330, a current control 340 and a set point setting
350.
[0083] The active power control 310 is set up to calculate an
angular velocity .omega. and an internal reference angle .THETA.
from this from an active power set point P_set, in particular for
the converter, which is specified by a wind power installation
control, for example.
[0084] For this purpose, the active power set point P_set is
firstly offset against an actual generator torque T_e and an
angular velocity .omega. is determined from this with the aid of a
frequency droop mechanism fdm.
[0085] The internal reference angle .THETA. is then determined for
the virtual synchronous machine from the angular velocity .omega.
using an amplification k.
[0086] The internal reference angle .THETA. then serves as an input
variable for the processing unit 330.
[0087] The reactive power control 320 is set up to calculate a
virtual excitation voltage v_vir_e from a reactive power set point
Q_set, in particular for the converter, which is specified by a
wind power installation control, for example, and a detected
reactive power Q_mea, which virtual excitation voltage serves as an
input variable for the processing unit 330.
[0088] In addition, a voltage control vdc is provided inside the
reactive power control, which voltage control compares a voltage
V_PCC_mea detected at the converter output with a voltage target
specification V_PCC and can be connected by means of the switch
S1.
[0089] The processing unit 330 is further set up to calculate a
virtual pole wheel voltage e* from a or the virtual excitation
voltage v_vir_e, in particular of the reactive power control 320, a
or the angular velocity .omega. and a or the internal reference
angle .THETA..
[0090] Current set points S* are then calculated for the converter
from this virtual pole wheel voltage e* by means of the current
control 340, for example for a tolerance band method by means of
which the converter 200 is controlled.
[0091] In further embodiments, further set point settings Set_1,
Set_2 can additionally be provided in order to further optimize
operation of the virtual synchronous machine.
[0092] FIG. 2 shows a control module (circuit) 1000 of a converter
in an embodiment.
[0093] In particular, the control module 1000 is set up to control
a converter in such a way that the converter emulates the behavior
of a synchronous machine.
[0094] The control module comprises a power module (circuit) 1100
and a correction module (circuit) 1200 for this purpose.
[0095] The power module 1100 has a detected power, in particular
detected at the converter output, as an input variable, in
particular an active power P_mea.
[0096] As described previously or hereinafter, the power module
calculates a power change dP/dt therefrom, in particular depending
on the detected power P_mea.
[0097] The power change dP/dt calculated in this way is supplied to
the correction module 1200.
[0098] The correction module 1200 calculates a power set point
P_set_corr or directly the power set point P_set for the converter
from the power change dP/dt, for example, if the power change dP/dt
exceeds a predetermined threshold value, for example.
[0099] The control module 1000 therefore preferably only intervenes
in the control of the converter, as in FIG. 1B, for example, if a
predetermined threshold value is exceeded, which indicates a loss
of angular stability.
[0100] In such cases, it is then proposed to control a smaller
power set point P_set or in particular to set the correction value
for the power set point P_set_corr by means of the correction
module.
[0101] In particular, it is therefore also proposed to reduce the
power output of the converter in the event of a loss of angular
stability.
[0102] FIG. 3 shows a control module 1000 of a converter, in
particular as shown in FIG. 2, in a preferred embodiment.
[0103] The control module 1000 additionally has a power angle
module (circuit) 1300.
[0104] The power angle module 1300 is set up to calculate a power
angle change d.delta./dt depending on the detected frequencies, in
particular the electrical frequency .omega._g of the electrical
supply network and the electrical frequency .omega._m of the
virtual synchronous machine.
[0105] The power angle change d.delta./dt calculated in this way is
then multiplied by the power change dP/dt by means of the
multiplication, in particular in order to obtain a coefficient PSC
which has the same sign as a power synchronizing coefficient. This
coefficient can also be described as a change in the power
according to the angle, i.e., dP/d.delta..
[0106] FIG. 4 shows a control module 1000 of a converter, in
particular as shown in FIG. 3, in a particularly preferred
embodiment.
[0107] In this case, the power angle module 1300 has at least one
summation (adder/subtractor) 1310 which is set up to compare at
least one first electrical frequency .omega._g with a second
electrical frequency .omega._m, in particular in order to calculate
a frequency difference (w).
[0108] In this case, the first electrical frequency is preferably
the electrical frequency of the electrical supply network .omega._g
and the second electrical frequency the electrical frequency of the
virtual synchronous machine .omega._m.
[0109] In addition, the power angle module 1300 has at least one
limiter 1320 which is set up to limit the frequency difference
.omega. to positive values. The limiter therefore preferably
operates between 0 and infinity.
[0110] In particular, it is therefore also proposed to only
consider positive values with regard to the power angle change
d.delta./dt.
[0111] For this purpose, the power angle change d.delta./dt is led
via a saturation block 1320 or limited to exclusively positive
values.
[0112] If negative values are therefore present, a zero is output
by the limiter or saturation block which results in the product of
the power angle change d.delta./dt and power change dP/dt also
being zero, whereby the threshold value of the correction module is
not exceeded and the set points P_set thus do not change, in
particular because there is a stable operation.
[0113] In particular, it is therefore also proposed that only the
situations in which the angle .delta. accelerates and the power P
decreases are identified as a critical state.
[0114] FIG. 5 shows a power module 1100 of a control module 1000,
as shown in FIGS. 2 to 4, for example, in a preferred
embodiment.
[0115] The power module 1100 comprises at least one discrete
implementation (discrete processor) 1110 and a discrete filtering
1120.
[0116] The power module 1110 is thus set up to calculate a
derivative of the power with respect to time from the detected
active power P_mea, in particular a power change dP/dt, which is
filtered by means of the discrete filtering 1120.
[0117] In particular, this means that the power module 1110 is set
up to determine the power change dP/dt with respect to time, in
particular as a differential.
[0118] In particular, a discrete implementation 1110 of the
derivative of the measured power P_mea is proposed for determining
this power change dP/dt, which implementation cooperates with an
additional cascaded discrete filtering 1120.
[0119] FIG. 6 shows a power module 1100 of a control module 1000,
as shown in FIGS. 2 to 4, for example, in a further preferred
embodiment.
[0120] The power module 1100 comprises at least one observer
1130.
[0121] The observer can be run by a PI controller, for example,
which acts on a difference between the measured power P_mea and an
estimated power P_est and calculates a state variable dP.sub.dt as
a result.
[0122] The control module makes it possible to avoid angular
instability in the virtual synchronous machine. This can arise, for
example, if an error occurs in a line and the equivalent impedance
between the converter and the network suddenly increases as a
result of switching off the affected line. The result of this is
that the set point power can no longer be transmitted due to the
physical limits of the system. This, in turn, causes the
synchronization with the network to be lost in a virtual
synchronous machine (as indeed in a synchronous machine). The
control module implements an additional controller which identifies
this critical state using available measured values and allows
appropriate measures to be taken, such as adjusting the power set
point, for example.
LIST OF REFERENCE NUMBERS
[0123] 100 wind power installation [0124] 200 converter, in
particular a power converter of a wind power installation [0125]
300 control unit of a virtual synchronous machine [0126] 310 active
power control, in particular for the converter [0127] 320 reactive
power control, in particular for the converter [0128] 330
processing unit, in particular of the virtual synchronous machine
[0129] 340 current control, in particular for the converter [0130]
350 set point setting, in particular for the converter [0131] 1000
control module [0132] 1100 power module [0133] 1110 discrete
implementation, in particular of the power module [0134] 1120
discrete filtering, in particular of the power module [0135] 1130
observer, in particular of the power module [0136] 1200 correction
module [0137] 1300 power angle module [0138] 1310 summation [0139]
1320 limiter [0140] 1400 multiplication (multiplier) [0141] e*
virtual pole wheel voltage [0142] fdm frequency droop mechanism
[0143] k amplification [0144] k_tresh predetermined threshold value
[0145] P_est estimated active power [0146] P_mea detected active
power [0147] P_set power set point, in particular for the wind
power installation [0148] P_set_corr correction value for the power
set point, in particular for the wind power installation [0149]
P_set active power set point setting, in particular for the
converter [0150] PSC coefficient or product [0151] Q_set reactive
power set point setting, in particular for the converter [0152]
Q_mea detected reactive power [0153] S1 switch [0154] S* current
set points, in particular for the converter [0155] Set_1 first
further set point setting [0156] Set_2 second further set point
setting [0157] T_e actual generator torque [0158] V_PCC voltage
target specification, in particular for the converter, at the
converter output [0159] V_PCC_mea voltage detected at the converter
output [0160] v_vir_e virtual excitation voltage, in particular
virtual excitation voltage [0161] vdc voltage control, in
particular voltage droop control [0162] .omega._g electrical
frequency of the electrical supply network [0163] .omega._m
electrical frequency of the virtual synchronous machine [0164]
dP/dt power change, in particular power change with respect to time
[0165] d.delta./dt power angle change, in particular power angle
change with respect to time
[0166] The various embodiments described above can be combined to
provide further embodiments. These and other changes can be made to
the embodiments in light of the above-detailed description. In
general, in the following claims, the terms used should not be
construed to limit the claims to the specific embodiments disclosed
in the specification and the claims, but should be construed to
include all possible embodiments along with the full scope of
equivalents to which such claims are entitled. Accordingly, the
claims are not limited by the disclosure.
* * * * *